'\" t
.TH "SD_EVENT_ADD_DEFER" "3" "" "systemd 257.1" "sd_event_add_defer"
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.SH "NAME"
sd_event_add_defer, sd_event_add_post, sd_event_add_exit, sd_event_handler_t \- Add static event sources to an event loop
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-event\&.h>
.fi
.ft
.sp
.ft B
.nf
typedef struct sd_event_source sd_event_source;
.fi
.ft
.HP \w'typedef\ int\ (*sd_event_handler_t)('u
.BI "typedef int (*sd_event_handler_t)(sd_event_source\ *" "s" ", void\ *" "userdata" ");"
.HP \w'int\ sd_event_add_defer('u
.BI "int sd_event_add_defer(sd_event\ *" "event" ", sd_event_source\ **" "source" ", sd_event_handler_t\ " "handler" ", void\ *" "userdata" ");"
.HP \w'int\ sd_event_add_post('u
.BI "int sd_event_add_post(sd_event\ *" "event" ", sd_event_source\ **" "source" ", sd_event_handler_t\ " "handler" ", void\ *" "userdata" ");"
.HP \w'int\ sd_event_add_exit('u
.BI "int sd_event_add_exit(sd_event\ *" "event" ", sd_event_source\ **" "source" ", sd_event_handler_t\ " "handler" ", void\ *" "userdata" ");"
.SH "DESCRIPTION"
.PP
These three functions add new static event sources to an event loop\&. The event loop object is specified in the
\fIevent\fR
parameter, the event source object is returned in the
\fIsource\fR
parameter\&. The event sources are enabled statically and will "fire" when the event loop is run and the conditions described below are met\&.
.PP
The
\fIhandler\fR
is a function to call or
\fBNULL\fR\&. The handler function will be passed the
\fIuserdata\fR
pointer, which may be chosen freely by the caller\&. The handler may return negative to signal an error (see below), other return values are ignored\&. If
\fIhandler\fR
is
\fBNULL\fR, a default handler that calls
\fBsd_event_exit\fR(3)
will be used\&.
.PP
\fBsd_event_add_defer()\fR
adds a new event source that will be dispatched instantly, before the event loop goes to sleep again and waits for new events\&. By default, the handler will be called once (\fBSD_EVENT_ONESHOT\fR)\&. Note that if the event source is set to
\fBSD_EVENT_ON\fR
the event loop will never go to sleep again, but continuously call the handler, possibly interleaved with other event sources\&.
.PP
\fBsd_event_add_post()\fR
adds a new event source that is run before the event loop will sleep and wait for new events, but only after at least one other non\-post event source was dispatched\&. By default, the source is enabled permanently (\fBSD_EVENT_ON\fR)\&. Note that this event source type will still allow the event loop to go to sleep again, even if set to
\fBSD_EVENT_ON\fR, as long as no other event source is ever triggered\&.
.PP
\fBsd_event_add_exit()\fR
adds a new event source that will be dispatched when the event loop is terminated with
\fBsd_event_exit\fR(3)\&.
.PP
The
\fBsd_event_source_set_enabled\fR(3)
function may be used to enable the event source permanently (\fBSD_EVENT_ON\fR) or to make it fire just once (\fBSD_EVENT_ONESHOT\fR)\&.
.PP
If the handler function returns a negative error code, it will either be disabled after the invocation, even if the
\fBSD_EVENT_ON\fR
mode was requested before, or it will cause the loop to terminate, see
\fBsd_event_source_set_exit_on_failure\fR(3)\&.
.PP
To destroy an event source object use
\fBsd_event_source_unref\fR(3), but note that the event source is only removed from the event loop when all references to the event source are dropped\&. To make sure an event source does not fire anymore, even when there\*(Aqs still a reference to it kept, consider setting the event source to
\fBSD_EVENT_OFF\fR
with
\fBsd_event_source_set_enabled\fR(3)\&.
.PP
If the second parameter of these functions is passed as
\fBNULL\fR
no reference to the event source object is returned\&. In this case the event source is considered "floating", and will be destroyed implicitly when the event loop itself is destroyed\&.
.PP
If the
\fIhandler\fR
parameter to
\fBsd_event_add_defer()\fR
or
\fBsd_event_add_post()\fR
is
\fBNULL\fR, and the event source fires, this will be considered a request to exit the event loop\&. In this case, the
\fIuserdata\fR
parameter, cast to an integer, is passed as the exit code parameter to
\fBsd_event_exit\fR(3)\&. Similar functionality is not available for
\fBsd_event_add_exit()\fR, as these types of event sources are only dispatched when exiting anyway\&.
.SH "RETURN VALUE"
.PP
On success, these functions return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-ENOMEM\fR
.RS 4
Not enough memory to allocate an object\&.
.RE
.PP
\fB\-EINVAL\fR
.RS 4
An invalid argument has been passed\&.
.RE
.PP
\fB\-ESTALE\fR
.RS 4
The event loop is already terminated\&.
.RE
.PP
\fB\-ECHILD\fR
.RS 4
The event loop has been created in a different process, library or module instance\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_event_add_defer()\fR,
\fBsd_event_add_post()\fR,
\fBsd_event_add_exit()\fR, and
\fBsd_event_handler_t()\fR
were added in version 217\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-event\fR(3), \fBsd_event_new\fR(3), \fBsd_event_now\fR(3), \fBsd_event_add_io\fR(3), \fBsd_event_add_time\fR(3), \fBsd_event_add_signal\fR(3), \fBsd_event_add_child\fR(3), \fBsd_event_add_inotify\fR(3), \fBsd_event_source_set_enabled\fR(3), \fBsd_event_source_set_priority\fR(3), \fBsd_event_source_set_userdata\fR(3), \fBsd_event_source_set_description\fR(3), \fBsd_event_source_set_floating\fR(3), \fBsd_event_exit\fR(3)
